Visual Impact Assessment Guidebook

Table of Contents

Visual impact assessment procedures

Visual impact assessments estimate, in perspective view, the potential visual effect of proposed operations on the scenic landscape. These assessments are used to confirm whether visual quality objectives for these sites will be achieved. This section describes a five-step process for completing a visual impact assessment and identifies the various products that are required as part of the VIA report.

Figure 5 The five-step visual impact assessment process.

In practice, the VIA process may not be carried out in such a straightforward sequence of steps as shown in Figure 5. Many aspects of steps 1 and 2 may have already been completed in developing the forest development plan. In addition, a certain amount of interactive work may be required to develop visual design options and test, through visual simulations, their ability to meet visual quality objectives. Refer to the Visual Landscape Design Training Manual to assist in designing various options for proposed operations.

The following pages describe in more detail the typical procedures and sequence of events for each step of the visual impact assessment process.

Step 1: Planning and pre-field trip preparation

The purpose of this step is to gather and transfer onto maps all of the information that is known prior to carrying out the fieldwork. It is also a good time to contact district staff to discuss any assessment uncertainties and confirm viewpoint selection.

• Consult the visual landscape database and mapping for the area of proposed operations. For each visual sensitivity unit where activities are proposed, record the attribute data (i.e., EVC [existing visual condition], VAC [visual absorption capability], VSC [visual sensitivity class or equivalent], and VQO [visual quality objective]) on the assessment summary form (Appendix 2).
• Contact the forest district office to discuss specific assessment requirements if a cutting system other than clearcutting or seed tree is proposed. Further information can be found in Visual Impacts of Partial Cutting (1997).
• Make a preliminary list of the locations from which the proposed operation may be visible (e.g., highway rest areas, recreation sites, and communities) and transfer them onto the map prepared for the assessment package. Complete the assessment from the viewpoint(s) that provide the best view of the land-form or unit on which the proposed operation is to occur. These viewpoints may or may not correspond to those shown on the visual landscape inventory map. Confirm the viewpoint(s) selection with the district office.
• Transfer information about the visual sensitivity unit boundary and existing landscape alterations, such as cutblocks and roads, to a 1:20 000 or larger- scale (e.g., 1:10 000 or 1:5000) topographic base map. This information will help to position and sketch the proposed operation on perspective photographic overlays. Identify the location of the proposed operation on the topographic base map.

Step 2: Conducting fieldwork

The purpose of the fieldwork is to gain an on-the-ground familiarity with the planning area from a visual perspective, to locate the pre-selected viewpoints, and to gather data. This step is also necessary to confirm whether these pre-selected viewpoints require updating on the basis of the actual viewing conditions.

• Conduct the assessment using the means of travel most often used by the average forest visitor or traveller (e.g., vehicle on roads, boat on water, or on foot).
• Locate the viewpoints identified in the office and select the one(s) that provides the best view of the proposed operation being assessed. Identify and number these viewpoints on the topographic base map (1:20 000 scale or larger). Familiarize yourself with the landscape and the proposed operation by travelling throughout the study area as much as possible, taking note of special features, road stops, viewpoints, traffic pull-offs, and traffic conditions.
• At each viewpoint:
  • Take a photograph, or a set of overlapping photographs, of the landscape to capture the entire landform where the operation is proposed. By off-setting the photo point by a few metres, a second shot of the same scene can provide a stereographic pair which, when viewed through a stereoscope, will provide a three-dimensional image that can be useful for landform analysis. Refer to Appendix 3 for photography and presentation criteria.
  • Complete the photography data section of the visual impact assessment summary form in Appendix 2.
  • Estimate the visible portion of the proposed operation on the topographic base map.
  • Back at the office, splice photographs together and label them (see Appendix 3).
  • Estimate and transpose the visible area of the proposed cutblock/road to the spliced photographs using the natural and human-made landmarks or features.

Step 3: Developing design options and preparing visual simulations

• Complete a visual force analysis on the sketch, photograph overlay, or digital terrain model (perspective view) and on the topographic base map (plan view). Refer to Appendix 4 for more in-depth information about this technique.
• Complete a land feature analysis on a photograph and on the topographic base map (plan view). Refer to Appendix 4 for more in-depth information about this technique.
• Using the results of the visual force and land feature analyses, develop one or more design options in perspective view exhibiting elements of good visual design. Development of more than one design option for each proposed operation may make the design and assessment process more efficient and cost-effective. Refer to the Visual Landscape Design Training Manual for more in-depth information about design techniques.
• Select the most appropriate technique (e.g. sketch, photographic manipulation, or computer model [see Appendix 5 for information about digital terrain models]) and prepare a visual simulation for each design option. This simulation will demonstrate what the proposed operation will look like from each of the viewpoints. Not every visual simulation technique is required for every assessment report (see Appendix 6 to choose an appropriate simulation technique). If any doubt exists as to the technique necessary for a given situation, consult the forest district office.
• In cases where hand simulations are produced, complete sight lines from major viewpoints to confirm how much of the proposed operation will be visible. Appendix 7 outlines procedures for plotting and presenting sight lines.
• Using the sight lines and field information, indicate on a 1:5000 or smaller- scale (e.g., 1:10 000, 1:20 000) topographic map that portion of the opening that would become visible following operations.

Step 4: Assessing visual simulations

The purpose of this step is to evaluate whether a proposed operation will achieve the established visual quality objective.

The evaluation is conducted at all important viewpoints. In addition, the existing non-visually effective green-up alterations within, and immediately adjacent to, the unit must be considered in this evaluation. Three variables are used to assess the visual simulation(s).

1. Basic VQO definition: Does a proposed operation meet the basic visual quality objective definition?
2. Visual design: Does a proposed operation exhibit elements of good visual design?
3. Numerical assessment: In perspective view, what proportions of the landform or unit are represented by existing non-visually effective green-up alterations and a proposed operation? What percent volume or stems will be left in the block? What level of site disturbance will be present?

In order to receive approval, it is imperative that all existing and proposed operations meet the basic VQO definition and exhibit elements of good visual design. The numerical assessment should be used only as a yardstick to help determine into which class the cumulative alterations on a landscape fall.

More detailed information about each of these variables is presented in the following subsections.

1. Visual quality objective definition

This is a measure of the ability of proposed operations, in combination with non-visually effective green-up alterations, to achieve the basic VQO definition. Table 1 presents an outline of these definitions.

Table 1 Visual quality objectives: five levels of landscape alteration

The assessment summary form in Appendix 2 outlines a process to evaluate and report on whether proposed operations will meet the visual quality objectives. This summarization will become an integral part of the assessment report.

2. Visual design of proposed operations

This is the measure of the ability of proposed operations to achieve the visual design concepts and principles as set out in the Visual Landscape Design Training Manual. Answering the following questions will help to guide the assessment.

• Have the major visual force lines been identified and used to develop the size and shape of the proposed operation?
• Has the proposed operation borrowed from the natural character of the landscape?
• Have edge treatments been incorporated into the design of the proposed operation (feathered edges, irregular cutblock design, etc.)?
• Have "islands," or patches of trees, been maintained to mitigate visual impacts and meet other resource management objectives?
• Have enough stems been left in the proposed partial cutblock to meet the established visual quality objective?

Key visual design concepts and principles

Incorporating the following important design concepts and principles into the planning of landscape- and stand-level forest development proposals will lead to better visual design. Refer to the Visual Landscape Design Training Manual for visual representations and more in-depth explanations of the principles presented below. The manual also provides additional concepts and principles.

Landscape-level cutblock design The following guidelines provide some clues for designing cutblocks at the landscape level based on internationally recognized design concepts and principles.

• Start in the less sensitive hollows and work up the hillside, when designing the first harvesting pass on a landscape.
• Locate larger openings on lower slopes and decrease the size of openings as the slope increases.
• Ensure that opening boundaries follow visual force lines by extending up hollows and descending down ridge lines.
• Design the shape of harvest units to reflect the quality of those shapes found in the natural landscape (i.e., rounded curvilinear shapes in rounded landforms; spiky jagged shapes in more rugged terrain).
• Use the visual cues presented by the landform, vegetation (timber types), and natural openings to determine the type of shape that is most appropriate for the particular landscape.
• Make sure that the general shape, scale, and position of the proposed operations fit the landscape. Organic shapes are generally more compatible with the natural landscape than geometric shapes.
• Design proposed operations with future passes or entries in mind to ensure that both visual quality objectives and wood removal can be maintained over the long term.
• Use curved lines rather than horizontal and vertical lines.
• Avoid jagged edges, right angles, and straight lines when designing opening boundaries. Where necessary use diagonal lines.
• Vary opening sizes and spacing between openings to achieve irregular appearance.
• Vary the texture on the landscape by introducing small cutblocks or by using partial cutting techniques.
• Protect Genius Loci, or the spirit of place.
• Make use of interlocking shapes like pieces of a jigsaw puzzle to improve the blending of proposed operations into the surrounding forest.
• Reduce contrasts in colour and shape of proposed operations to minimize their visual impact on the landscape.
• Design asymmetric cutblock shapes rather than symmetric ones (i.e., a large cutblock and a small one are better than two blocks of equal size and shape for a given landscape).
• Avoid creating notches or abrupt changes in tree canopy for openings proposed along skylines and ridge lines. If openings must cross a skyline, then they should cross in saddles or on breaks in ridge lines.
• Distribute openings between visible and non-visible areas, and between steeper and gentler slopes within visual sensitivity units.
• Use Table 2 as a broad guide for judging appropriate opening sizes in the landscape.

Table 2 A guide to determine appropriate opening size in perspective view at the landscape level

Stand-level cutblock design The following guidelines provide some clues for designing cutblocks at the stand level based on internationally recognized design concepts and principles. More information on these and additional concepts and principles can be found in the Visual Landscape Design Training Manual.

• Feather clearcut opening edges to reduce the sharp contrasting line between opening boundary and forest edge.
• Leave healthy, undamaged conifer and deciduous trees standing in well-designed clumps or in sufficient densities to break up an opening, reduce its apparent size, and avoid blowdown.
• Remove damaged, leaning, or poor-quality, residual trees in foreground views to avoid a scruffy appearance.
• Avoid leaving individual trees standing on ridge lines when these trees are viewed against the sky.

Road design The following guidelines provide some clues for designing roads on the landscape based on internationally recognized design concepts and principles. More information on these and additional concepts and principles can be found in the Visual Landscape Design Training Manual.

• Design road lines to curve gently and blend with the landform by climbing in hollows and dropping on ridge lines.
• Design road locations to make as much use of landform as possible and take advantage of non-visible areas, benches, and vegetative screening wherever possible to reduce visual effects.
• Align roads diagonally to slopes in those situations where mid-slope roads cannot be avoided; vary alignment in response to landform.
• Reduce the visual effects where roads cross skylines by locating them in hollows.
• Curve road lines gently to blend with natural landforms, dropping on convex slopes and rising in hollows.
• Locate roads away from skylines.
• Locate switchback roads on benches or in hollows, where possible, to minimize road cuts.
• Avoid locating roads that follow the viewers’ line of sight on gentle foreground slopes; roads should curve away or cross at another angle.
• Reduce the size of cut-and-fill slopes to decrease contrast between a road and the landscape.
• Use techniques such as end-hauling and controlled blasting to mitigate the visual effects of road construction on steep, visually sensitive slopes.
• Hydro-seed exposed mineral soil created by road construction or modification to reduce visual impacts.

3. Numerical assessment

The numerical assessment provides a measure of the ability of a proposed operation to achieve the numerical standards that predict a VQO. Percent alteration is used to assess the impact of clearcutting, volume or number of stems removed is used to assess partial cutting, and the level of site disturbance within a cutblock is used to assess the impact of roads.

Clearcutting: Percent alteration

Percent landform (unit) alteration is a reasonable predictor of achieved visual condition. To achieve a specific visual quality objective, this measure should fall within the ranges presented in Table 3 for those units harvested using a clear-cutting or seed-tree system. Factors that can influence the appropriate position within each alteration range include: visual absorption capability, slope, viewer position, viewing distance, quality of design, and number of residual trees.

If the other two variables are dealt with satisfactorily, an acceptable rationale can be submitted to support alterations beyond this range. Larger cutblocks may be accepted and approved if appropriate design principles and techniques are employed and these cutblocks meet the basic definition for the visual quality objective.

The following describes the general steps for making a numerical assessment of a clearcut. Refer to Appendix 8 for a more detailed account of the calculation procedures for percent alteration.

Use a planimeter or computer digitizer to measure (in perspective view) the visible landform unit that contains the proposed clearcut or seed-tree operation and to determine the size and scale of the operation itself. Include all previous operations that have not yet achieved visually effective green-up.

• Use the visual simulation product produced (i.e., sketch, photographic overlay, digital terrain model, or digital photo retouch) to perform the calculation. Do not use dot grids as these produce extremely unreliable results.
• Calculate, with this information, the percentage of the visible area being altered and compare this with the percentages of alteration allowed by the visual quality objective in the Table 3. Perform this calculation for each of the viewpoints selected for design and simulation and enter the results on the assessment form (Appendix 2).

Table 3 Predicting visual quality objectives based on percent alteration only (for clearcut and seed-tree silvicultural systems). Shaded areas indicate the most probable range for predictions based on percent alteration in perspective view only.

^a These percentages apply to the visible green portion of the landscape in perspective view. Rock and ice patches are excluded from the calculation.

Partial cutting: Volume or stems removed

Partial-cutting silvicultural systems must also be designed and carried out to meet established visual quality objectives. Partial-cutting systems always result in the retention of some volume or basal area on a cutblock. The net result is a change in the forest canopy texture. On cutblocks where a very low volume or basal area is removed, the change in texture is minimal. On cutblocks with a high level of removal, the texture becomes coarser. In situations where the removal rate is such that the ground becomes readily visible (e.g., seed-tree operations), the public no longer see a partial cut; they perceive a clearcut with only a few trees left.

Table 4 shows the likelihood of achieving a VQO for various combinations of volume or stems removed by tree height. Within the 10–40 m tree height range,
a 90% confidence of achieving the VQO is shown. For example, if 50% of the volume is removed for a tree height of 30 m, Table 4 shows that 90% of the time you will achieve partial retention. In some circumstances, the number of stems or volumes proposed for removal will fall outside of the data presented in this table, but will still achieve the visual quality objective.

Table 4 Predicting visual quality objectives using even-distribution, leave-tree, partial-cutting silvicultural systems^a.
Column values across top = mean height (m) of residual trees.
Row values down left = volume (stems) removed (%).

^a To use this table: First determine what percent of the stand you wish to remove, either in volume or by stems, along
Y-axis. Then determine the mean tree height of your stand along X-axis. Follow volume (Y) axis across and the tree height (X) down; their intersection point will yield the VQO you will most likely achieve.

^b R = retention; PR = partial retention; M = modification. See Table 1 for definitions of visual quality objectives.

Table 4 is based on the assumption that each stem proportionately contributes an equal volume to the stand. The data presented here were derived from forest stands with the following characteristics:

• slope: 3–47%;
• dbh: 17.5–86.3 cm;
• tree height: 11–39 m;
• pre-harvest volume: 70–844 m³/ha;
• pre-harvest basal area: 21–68 m² per ha; and
• pre-harvest stems: 136–1150 per ha.

Note: Use caution when extrapolating beyond these parameters.

Table 6 in the report Visual Impacts of Partial Cutting provides a much more detailed breakdown on both volume and stems removed. In addition, the report provides some guidance (see its Table 5) on use of basal area for achieving visual quality objectives. As long as a sufficient number and distribution of overstorey trees are retained to meet the visual quality objective, no maximum opening size is specified for partial-cut areas.

Observing the following guidelines will help to achieve the visual quality objective.

• Leave more volume and stems as the size of a partial-cut area increases.
• Leave more stems or volume as the slope increases.
• Leave more stems or volume in foreground views.
• Leave more stems or volume as visual absorption capability decreases.
• Maintain the integrity of ridge lines; ensure that an adequate number of stems, basal area, and volume are left on ridges to avoid a ragged appearance.
• Leave more volume and stems where windthrow is a problem.
• Design partial cuts so that a natural-appearing boundary remains. This is particularly important for even-aged stands, for openings that lie in snowbelt areas, and for areas where a high percentage of overstorey trees has been removed.
• Use low ground pressure, cable or aerial yarding systems on steep visible slopes.

Note: Observer position (i.e., above, level, or below the unit being viewed) can influence the number of stems or volume that must be left.

Appendix 9 contains a set of photo sheets that provide visual resource management practitioners with examples of the range of impacts acceptable for and within each visual quality class/objective category.

Roads and other site disturbances

Roads and other site disturbances can create some of the most severe and longest-lasting visual impacts on the landscape, unless carefully designed, constructed, and maintained.

Guidelines for designing roads on the landscape are presented earlier in this guidebook (see Step 4: "Visual Design of Proposed Operations" in the "Visual Impact Assessment Procedures" section). Table 5 identifies the amount of site disturbance found to be socially acceptable within a cutblock.

Table 5 Acceptable amount of visible roads and other site disturbances within a cutblock by visual quality objective

^a The allowable percent disturbance figures presented here are based on very preliminary research done in this subject area. These data will be refined with public perception research in the near future.

Important considerations related to Table 5:

• A cutblock that meets a visual quality objective from a definition and design standpoint could create a visual impact beyond the target VQO because of excessive roads and other visible disturbances.
• Factors that may affect visually acceptable levels of site disturbance include:
  • depth of disturbance in the ground,
  • composition of subsurface material,
  • soil colour, and
  • susceptibility to erosion or mass wasting.
• For scenic areas without VQOs, consideration is required to minimize the contrast created by roads and site disturbance.

Step 5: Preparing a visual impact assessment report

A recommended visual impact assessment report format and content is described below. Following this format will ensure consistency and may accelerate the review and approval process where the district manager has requested to see an assessment or the assessment is to be presented publicly. The assessment report or package should be self-contained and must be completed before the silviculture prescription is approved or before a road layout and design is submitted for approval. Where districts have standard operating procedures for visual resource management, district managers may wish to provide specific direction as to their requirements.

While there are many factors influencing the type and amount of information needed in a visual impact assessment report, the following basic information is considered essential to any report.

Basic content

1. Topographic map (1:50 000 or larger scale) showing:
   • Visual sensitivity unit boundaries from visual landscape inventory.
   • Visual sensitivity class (old VSR), visual absorption capability, existing visual condition, and established visual quality objective ratings for each unit.
   • Viewpoint / photo point locations and number.
   • Visible areas as seen from viewpoints.
   • Existing blocks and roads in and around the area proposed for development and the year logged.
   • Proposed blocks and roads and year to be harvested.
2. Pre-operations colour photograph(s) from important viewpoints (minimum size: 4 x 6").
3. Visual simulation product (sketch, photo, digital terrain model, or hybrid) showing proposed operations.
4. Completed visual impact assessment summary form (Appendix 2).

Note: The form has enough space for four viewpoints only. If an assessment involves more than four viewpoints, use additional copies of this summary form to capture all data.

Additional content

Depending on the visual sensitivity class, visual quality objective, number of viewpoints, complexity of the proposed operations, and/or silvicultural system proposed, additional supporting information may be required to accompany the assessment report (see Table 6).

Table 6 Additional supporting materials for visual impact assessment reports